purpose. The PR2000 (Topcon, Tokyo, Japan) is a photorefractor that has been
used in a population study comparing different methods of screening
preschool children. The present study was conducted to determine the
accuracy of the device in a largely clinical population.

methods. Two hundred twenty-two children less than 8 years of age were included.
All children were examined by an orthoptist using the PR2000 without
inducing cycloplegia. All children then underwent retinoscopy with
cycloplegia by an examiner who was unaware of the results from the
PR2000 examination.

results. The PR2000 gave a numerical reading for 90% of the children’s right
eyes and the message “Out of range” for a further 5%. The readings
underestimated the amount of hypermetropic or astigmatic refractive
error found on retinoscopy by an amount proportional to the magnitude
of the refractive error. Agreement with retinoscopy for the axis of
astigmatism more than 0.75 D was moderately good (intraclass
correlation coefficient [ICC] = 0.63). The PR2000 was more useful as
a screener, especially for anisometropia for which it was 91%
sensitive and 92% specific. The repeatability was good for sphere
(ICC = 0.74), less so for astigmatism (ICC = 0.59), and
better than the optometrist for anisometropia (ICC = 0.38). The
presence of nonrefractive diagnoses and the age of the children
examined made little difference in the screening results.

conclusions. The PR2000 underestimated hypermetropic refractive errors when used
without cycloplegia. However, it was at least as good a screening
device as other similar instruments, especially when judged by its
ability to detect anisometropia and the repeatability of the
results.

Automated refractors have become commonplace tools for the
examination of adult patients. Their effectiveness is well
characterized, and an optometrist performing a subjective refraction
frequently uses one to estimate errors before refinement.1 In recent years, several devices have been developed for use in young
children. Some have been proposed as suitable instruments for use in
screening programs, to detect children with or at risk for amblyopia or
strabismus associated with high refractive errors.2345678 Other studies have found less favorable results.9101112

The PR2000 Pediatric Refractometer (Topcon, Tokyo, Japan) was designed
for use in young children and was included in a longitudinal study of
infant visual development, as a potential tool for preschool vision
screening.13 The purpose of this study was therefore to
assess the accuracy and repeatability of readings obtained with the
PR2000.

Materials and Methods

Two hundred twenty-two children were recruited into the study.
Some (n = 68) were recruited from an ongoing population
study of infant development. The remainder were children attending a
hospital pediatric clinic (n = 154). All children were first
examined by an orthoptist who conducted a cover test and then used the
PR2000. Cyclopentolate drops (1.0%) were then instilled in each eye.
After at least 20 minutes, eyes were refracted by an experienced
pediatric optometrist who was unaware of the results obtained with the
PR2000. If the retinoscopy reflex was not stable, the optometrist
waited another 10 minutes, or until it was stable. Twenty-eight
children who lived locally were re-examined using the same protocol, 1
week later. The examiners did not have access to their previous
findings. Nineteen children were examined by an experienced user and by
an inexperienced user, on the same day, each unaware of the other’s
results. The study was performed in accordance with the Declaration of
Helsinki. All the parents accompanying the children had the purpose of
the study explained and gave their consent.

The PR2000 is a video-enhanced, infrared photorefractor and was used in
accordance with the manufacturer’s instructions. The child was seated
either alone or on a parent’s lap, at a distance of 0.9 m from
the machine in a darkened room. Built-in flashing red and green lights
and a beeping sound were used to attract the child’s attention. The
operator observed the image of the child’s face in the video screen
and slid the machine forward or backward so that the pupil margins were
clearly in focus. Both eyes were assessed simultaneously, unless there
was an obvious strabismus, when monocular readings were taken. The
PR2000 produced printouts with the refraction for each eye expressed as
sphere, negative cylinder, and axis. There were confidence scores
indicating which readings were estimated by the software to be very
reliable (the average of at least three recordings; denoted by a star),
unreliable (denoted by brackets) or moderately reliable (single
readings only; no star, no brackets). The machine stored the images
used for calculation for each subject. The measurable range was −5.0 D
to +5.0 D for sphere and cylinder, in 0.25 steps. Estimations outside
this range were denoted by error codes ≪+≫ or ≪−≫. Images that
could not be analyzed by the software were denoted by the message
ERROR. Axis determination was in gradations of 5°. The PR2000 showed
warning messages of “Room Light up” or “Room Light down” if the
ambient light levels needed adjustment. These instructions were
followed on the rare occasions when they occurred. In accordance with
the manufacturer’s instructions, readings for sphere of −1.00
D or more have had 1.0 added, to take account of the child’s
accommodation to a target at 1 m. This results in a dead zone of
between 0.0 D and −1.25 D, in which range there are no readings. For
uniocular measures, only the right eyes from each individual have been
analyzed. The statistical methods used were regression analysis,
calculation of the intraclass correlation coefficient (ICC), the
unweighted κ statistic, the sensitivity and specificity, and the
positive (PPV) and negative (NPV) predictive values.

Results

Results are means ± SD. The median age and interquartile
range for the 222 children were 48.2 months and 12.5 to 68.7 months,
respectively. The ethnicity of the children was not recorded. but
almost all were white (over 90%) The nonrefractive conditions
present were manifest strabismus (n = 35), lens
opacities (n = 5), pseudophakia
(n = 2), poor fixation (n =
13), nystagmus (n = 1), corneal scarring
(n = 1), or iris coloboma (n =
1). For 48 children, accurate times were recorded for the instillation
of drops and retinoscopy; the time between the two was 33 ± 5.9
minutes, and the range was 29 to 63 minutes.

Thirteen children (6%) registered ERROR and 10 children (5%)
registered “Out of range,” for the right eye. Of the remaining 199
right eye readings, 136 (68%) were “confidence 1, reliable,” 39
(20%) were “confidence 2, moderately reliable,” and 24 (12%) were“
confidence 3, poor reliability.” Readings (confidence 1–3) for
both eyes were obtained for 189 children. Four children (2%) had error
readings in both eyes. There was no difference in the magnitude of the
differences between PR2000 and retinoscopy for any of the three
confidence scores, for either spherical refractive errors (analysis of
variance [ANOVA], df = 2, F ratio = 1.77, P = 0.17) or for astigmatism (ANOVA, df= 2, F ratio = 2.04, P = 0.13).
Therefore, the data are presented for confidence readings 1 through 3
combined for the right eye (n = 199) for uniocular
measures of accuracy, and for the children with confidence results 1
through 3 in both eyes (n = 189) for the results concerning
anisometropia and screening.

Spherical Refractive Error

The PR2000 and cycloplegic retinoscopy readings for the spherical
refractive error of the right eye were compared, and Figure 1 shows the differences between the two measurements plotted against the
mean of the two measures. The mean difference between retinoscopy and
the PR2000 was 1.16 ± 1.52 D. As Figure 1 shows, the differences
between the two measures were related to the mean magnitude of the
hypermetropic refractive error (r = 0.67, r2 = 0.45, P <
0.001).

Anisometropia

The estimates of the PR2000 and the optometrist for the amount of
anisometropia present were compared; Figure 2 shows a plot of the differences in anisometropia against the mean of
the two values. The mean difference between the PR2000 and retinoscopy
was 0.01 ± 0.83 D. However, in Figure 2 there is still a relation
between the difference and the mean value (r = 0.53, r2 = 0.28, P <
0.001), even when the outlying point is excluded (r =
0.38, r2 = 0.15, P <
0.001).

Astigmatism

When inspected on a scatter plot (not shown), the data were
approximately symmetrically distributed around the line of perfect
agreement, and the mean difference between the two methods was−
0.1 ± 0.61 D. There is again a relation between the differences
and the mean value; r = 0.57, r2 = 0.33; P < 0.001.
The axis of astigmatism was first assessed categorically, according to
the direction of the positive component: with-the-rule if between 61°
and 120°, against-the-rule if between 0° to 30° or 151° to
180°, and oblique for all other directions. Cases in which there was
no astigmatic error were classified as none. For all 199 cases, the
unweighted κ statistic (95% confidence interval [CI]) for
agreement between the PR2000 and cycloplegic retinoscopy was κ =
0.33 (0.23–0.42). For 32 cases in which the PR2000 estimated the
astigmatism as more than 0.75 D, the agreement with the optometrist was
better (κ = 0.68, 0.45–0.90). The ICC for actual measurements
of the axis was 0.20 for all 199 cases but increased to 0.63 for the 32
cases with more than 0.75 D astigmatism.

Children with and without Nonrefractive Diagnoses

The proportion of error readings in the right eye was 3 (5%) of
58 for the children with nonrefractive diagnoses, compared with 10
(7%) of 164 for the children with refractive errors only
(P = 0.54, Fisher’s exact test). The proportion of
out-of-range values was 6 (10%) of 58 for the children with
nonrefractive diagnoses, compared with 4 (2%) of 164 for the children
with refractive errors only (P = 0.02, Fisher’s exact
test). Of the 189 children with results (confidence 1–3) for each eye,
there were 35 children with nonrefractive problems (31 with strabismus,
2 with lens opacity, 1 with corneal scarring, and 1 with pseudophakia).
The mean differences between the PR2000 and the retinoscopy results
were larger for the children with nonrefractive problems than for the
children with refractive errors alone. The differences were 1.8 ±
1.9 D versus 1.0 ±1.4 D for sphere, 0.29 ± 0.57 D versus
0.13 ± 0.62 D for astigmatism and 0.09 ± 0.83 D versus
0.008 ± 0.83 D for anisometropia. The only statistically
significant difference between the two groups was in the results for
sphere (ANOVA, df = 1, F ratio 7.8, P =
0.006). The differences were still related to the mean quantity
measured, for all parameters in the children with refractive errors
only and for the measurement of spherical error in the children with
nonrefractive problems (ANOVA, df = 1, P <
0.001 in all cases).

Accuracy of the PR2000 for Different Age Groups

The 189 children with full results were classified into age
groups: up to 36 months (n = 83), 36 to 59 months (n= 45), and more than 59 months (n = 61). The mean
differences between the spherical refractive errors, measured by
retinoscopy, compared with those measured with the PR2000 for the three
age groups were; 0.84 ± 1.3 D, 1.3 ± 1.7 D, and 1.5 ±
1.6 D for children aged less than 36 months, 36 to 59 months, and more
than 59 months, respectively (ANOVA, df = 2, F ratio =
3.8, P = 0.02). The only statistically significant
individual difference was between the results for children aged less
than 36 months compared with those for children aged more than 59
months (P = 0.02). The corresponding ICCs for agreement
between the PR2000 and retinoscopy for sphere were 0.35, 0.61, and
0.59, respectively. The range of the retinoscopic errors for children
aged up to 36 months was −1.25 to +7.5 D; for children 36 to 59
months, −4.5 to +7.75 D; and for children above 59 months, −5.5 to+
6.7 D.

Repeatability of the PR2000 and of Cycloplegic Retinoscopy

The results estimating the repeatability of the PR2000 and of
cycloplegic retinoscopy by the optometrist are shown in Table 1 . The ICC values suggest that the PR2000 was less repeatable for
sphere, spherical equivalent, and astigmatism but was more repeatable
for anisometropia than was retinoscopy. However, the differences in
measures between visits are smaller for the PR2000 than for
retinoscopy, except those relating to astigmatism. This discrepancy
between the ICC and the magnitude of the differences is likely to be
because the ICC is affected by the range of values, which was greater
for the retinoscopy data than for the PR2000 data. The ICC for axis
determination was 0.92 for the PR2000 and for retinoscopy was only
0.04. However, of the nine cases in which there was retinoscopic
astigmatism on both occasions, six axes agreed exactly: one differed by
20°, one by 85°, and one by 175°. Of the eight cases in which the
PR2000 detected astigmatism on both visits, seven axes agreed within
10° and 1 by 40°. The unweighted κ statistics for the
repeatability of classification of the axis of astigmatism (with the
rule, against the rule, or oblique), were κ = 0.75 for the
PR2000 and κ = 0.64 for the optometrist.

Nineteen children were examined with the PR2000 by a trained user and
by a completely inexperienced user on the same day. The mean agreement
between the two users for the right eye results was 0.03 ± 0.14 D
for spherical refractive error and 0.05 ± 0.17 D for astigmatism.

Accuracy of the PR2000 as a Screening Tool

Receiver operating characteristic (ROC) curves demonstrating the
sensitivity and specificity of the PR2000, using different cutoff
points for referral, are shown in Figures 34and 5 (for 189 children with full data). When screening is conducted
for a relatively rare condition, cost considerations may necessitate
using a very specific referral cutoff for the screening test, to avoid
large numbers of overreferrals. Table 2 shows the results that were obtained, either when the sum of
sensitivity + specificity was the greatest of those tested, or when the
specificity was required to be 95% or greater. The sensitivities
decline, but the PPV values increase, when the specificity is required
to be at least 95%. Screening for anisometropia was more accurate than
screening for hypermetropia or astigmatism in both situations.

Nonrefractive Diagnoses and the Age of the Subjects

The calculations in Table 2 were repeated with the exclusion of
the 35 children with nonrefractive diagnoses. When the more specific
(at least 95%) referral cutoffs are used, as shown in Table 2 , the
sensitivities, specificities, PPV, and NPV for hypermetropia were 54%,
95%, 76%, and 92%, respectively. The corresponding percentages for
anisometropia and astigmatism were 69%, 96%, 65%, and 96% and 50%,
97%, 75%, and 91%, respectively, which are similar to those in Table 2 . Repeat calculations were performed with the children divided into
three subgroups according to age (Table 3) . For all three target refractive errors, the PPV values were lower in
the younger children; otherwise, there were few differences between
groups.

Discussion

The PR2000 provided useful data for 98% of the children and a
full set of numerical data for each eye in 85%. The differences
between the PR2000 and retinoscopy were related to the quantity
measured and tended to underestimate any hypermetropia present. This
was not unexpected. The PR2000 was used without cycloplegia, as would
be practicable in a preschool screening program, whereas the
retinoscopy was performed after cycloplegia. Previous studies have
found a similar result.9

Many of the children had other diagnoses besides suspected refractive
error. The differences between the PR2000 and retinoscopy were larger
for the children with nonrefractive diagnoses, although this was only
statistically significant for the measurement of spherical refractive
error. This might be expected, because many of these children had
strabismus and may have a strong tendency to overaccommodate, which
would mask any hypermetropic error in noncycloplegic conditions.
However, the screening results for the PR2000 were similar whether the
children with other problems were included or excluded.

There was no consistent effect of the age of the child on the accuracy
of the PR2000. Although the differences between the PR2000 and the
retinoscopy results for sphere were smaller for the youngest children
(aged <36 months) than for the oldest children (aged >59 months), the
ICC for agreement with retinoscopy was only 0.35 for the youngest
children, whereas that for the other two categories was approximately
0.60. This apparent disagreement may be because the range of refractive
errors was smaller in the youngest children. Because examination by the
PR2000 requires very little cooperation from the child except brief
fixation on the target, it is not surprising that age made little
difference in these results. The PPV values for screening the younger
children were less than those for the older two groups (Table 3) , but
the prevalence of target conditions was also lower in this group, which
would reduce the PPV.

The ROC curves and the data in Tables 2and 3 indicate a more accurate
profile for the PR2000 when screening for anisometropia than when
screening for spherical or astigmatic errors. This might be expected,
because both eyes were measured simultaneously. There are few data in
the literature with which to compare these data, but a custom-built
device detected both of two cases of more than 2.0 D anisometropia,
whereas four infants with anisometropia between 2.0 and 1.5 D were
missed, in a sample of 97 infants. These data suggest a lower
sensitivity than found for the PR2000.3

The data in Tables 2and 3 for hypermetropia and astigmatism also
compare well with the results of screening obtained using other devices
in children without cycloplegia. For the group using a custom-built
device, the sensitivity was 85% and specificity only 53%,when
screening for hypermetropia in excess of 3.25 D,14 compared with 80% and 82%, respectively, in the present study (Table 2) . Another group, using the VPR-1 (Clement Clarke, Harlow,
UK), found that the sensitivity was only 12%, but with 99%
specificity, when screening for hypermetropia of 4 D or more, whereas
for astigmatism of more than 1.75 D, sensitivity was 54% and
specificity was 62%.10 The equivalent percentages in this
study were 94% sensitivity and 75% specificity (Table 2) . In two
recent studies on the MTI photoscreener (Medical Technologies, Riviera
Beach, FL), there was marked variability between different operators in
the accuracy of grading the pictures.1215 In one of these
studies, no individual grader achieved sensitivity and specificity both
above 70%.15 In the present study the PR2000 achieved
this for all target conditions (Table 2) . The Retinomax autorefractor
(Nikon, Tokyo, Japan) had a sensitivity of 70%, specificity of 95%,
PPV of 79%, and NPV of 92%, respectively, for hyperopia of 3.5 D or
more in children aged 9 to 36 months.8 These values
suggest slightly greater sensitivity than the present study (Tables 23) . The percentages for astigmatism of more than 2 D detected with
the Retinomax were 59% sensitivity and 95% specificity, with PPV of
71% and an NPV of 92%,7 which again are slightly more
sensitive but otherwise very similar to the results in the present
study (Tables 23) .

The retinoscopy results were very repeatable, except those for
anisometropia, for which the ICC was surprisingly low. However, this
repeatability study was small, and the results should be interpreted
cautiously. Although generally less repeatable than retinoscopy, the
results for the PR2000 (Table 1) compare favorably with those given for
the VPR-1, with which the mean difference between visits for assessment
of spherical refractive error was 0.12 ± 1.1 D and for
astigmatism was 0.2 ± 1.6 D.9 The repeatability
reported for the Retinomax was also worse than that found in the
present study for sphere, with a mean difference between refractions of
0.05 ± 1.33 D. The results were similar to those in the present
study for astigmatism; however, with a mean difference between
refractions of 0.04 ± 0.45 D.7 Autorefractors used
in adults with pseudophakic eyes can be more repeatable: 0.04 ±
0.30 D for sphere and 0.02 ± 0.36 for astigmatism.16

Cycloplegic retinoscopy was the gold standard against which we judged
the results from the PR2000. The results may differ from those that
would have been obtained when comparing the PR2000 results with those
of subjective refractions in subjects without cycloplegia. The use of
cycloplegic drops introduces further variability. It is possible that
the use of a variable gold standard reduced the apparent accuracy of
the PR2000. Alternatively, if cycloplegia had not been fully induced,
in many children it would have led to an increased estimate of the
sensitivity of the PR2000 for hypermetropia. These caveats also apply
to the other studies quoted in which cycloplegic retinoscopy was
used,34789121415 and therefore comparisons may still
be made between the different devices tested.

In our institution, the most experienced retinoscopist was the senior
hospital optometrist, who performed the refractions in this study, but
different institutions may have other professionals who perform most of
the retinoscopy. Many of the children were selected from hospital
clinics, and the results therefore cannot be generalized to normal
populations. Similarly, the results apply to a predominantly white
population and may not be applicable in areas in which there is a much
higher prevalence of children with heavily pigmented eyes. The PR2000
also provides an estimate of ocular alignment based on the corneal
reflections. This feature was not assessed, because the PR2000 was not
used in this respect in our longitudinal study. An earlier prototype of
the PR2000 (the PR1100) was validated in this regard and found to be
reliable but to have poor agreement with the results of a prism cover
test.17

The current results suggest that the PR2000 provides repeatable
results, has a more accurate screening profile than some devices in the
literature (the VPR-1 and the MTI) and a comparable (although slightly
less sensitive) profile to that of the Retinomax for sphere and
astigmatism. However, the most accurate results were obtained when
screening for anisometropia, and few comparable data were found for the
other devices. Anisometropia may be labile in childhood,18 and the nature of the relation between anisometropia and strabismus or
amblyopia is as yet unclear.19 Nevertheless, anisometropia
is strongly associated clinically with strabismus and/or
amblyopia.20 When used in our main population study in
children less than 37 months of age (results presented separately), the
PR2000 was more sensitive than was visual acuity testing, especially
when detecting straight-eyed amblyopia, which is commonly associated
with anisometropia. In conclusion, the PR2000 was a reliable device,
most accurate when assessing anisometropia but with sufficient
sensitivity and specificity for other refractive errors to be of
potential use in research or screening programs.

Supported by funding from the South West Regional Health Authority and the National Eye Research Centre. CW was the recipient of a Medical Research Council Training Fellowship.

Percentages for Sensitivity, Specificity, PPV, and NPV for the PR2000,
Using Different Criteria to Set the Referral Level

Table 2.

Percentages for Sensitivity, Specificity, PPV, and NPV for the PR2000,
Using Different Criteria to Set the Referral Level

Criterion

Target

Prevalence of Target Error (%)

PR2000 Referral Level (Diopters)

Sensitivity

Specificity

PPV

NPV

Maximum sum of sensitivity+ specificity

Spherical error > 3.75 D

19

1.5

80

82

51

95

Anisometropia > 1.25 D

12

1.0

91

92

62

99

Astigmatism > 1.25 D

16

0.75

94

75

43

98

Specificity at least 95%

Spherical error > 3.75 D

19

2.0

49

95

68

90

Anisometropia > 1.25 D

12

1.25

74

95

65

96

Astigmatism > 1.25 D

16

1.25

48

96

71

90

Sensitivity is the proportion of true cases correctly identified,
and specificity is the proportion of true normal subjects correctly
identified by the screening test. PPV is the proportion of referrals
from the screening test that truly have the target condition and NPV is
the proportion of individuals passed by the screening test who are free
of the target condition. n = 189.

Percentages for Sensitivity, Specificity, PPV, and NPV for the PR2000,
Using Different Criteria to Set the Referral Level

Table 2.

Percentages for Sensitivity, Specificity, PPV, and NPV for the PR2000,
Using Different Criteria to Set the Referral Level

Criterion

Target

Prevalence of Target Error (%)

PR2000 Referral Level (Diopters)

Sensitivity

Specificity

PPV

NPV

Maximum sum of sensitivity+ specificity

Spherical error > 3.75 D

19

1.5

80

82

51

95

Anisometropia > 1.25 D

12

1.0

91

92

62

99

Astigmatism > 1.25 D

16

0.75

94

75

43

98

Specificity at least 95%

Spherical error > 3.75 D

19

2.0

49

95

68

90

Anisometropia > 1.25 D

12

1.25

74

95

65

96

Astigmatism > 1.25 D

16

1.25

48

96

71

90

Sensitivity is the proportion of true cases correctly identified,
and specificity is the proportion of true normal subjects correctly
identified by the screening test. PPV is the proportion of referrals
from the screening test that truly have the target condition and NPV is
the proportion of individuals passed by the screening test who are free
of the target condition. n = 189.